//#pragma GCC optimize("Ofast,unroll-loops,O3")
//#pragma GCC target("avx,avx2,sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,fma,tune=native")
#include<bits/stdc++.h>
//#include<bits/extc++.h>
//#pragma pack(1)
#define fast ios::sync_with_stdio(0); cin.tie(0);
#define int long long
#define pii pair<int,int>
#define x first
#define y second
#define N 115
using namespace std;
//using namespace __gnu_pbds;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
//typedef tree<int, null_type,less_equal<int>, rb_tree_tag,tree_order_statistics_node_update> order_multiset;
//typedef tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update> order_set;
int n,k;
pii arr[N];
long double dp[N][N][N],ans=1e100;
bool vis[N];
vector<pii>tog,all;
long double solve(int use){
for (int i=0;i<=n;i++){
for (int j=0;j<=n;j++) dp[0][i][j]=1e18;
}
dp[0][0][0]=0;
for (int i=1;i<=n;i++){
for (int j=0;j<=n;j++){
for (int h=0;h<=use;h++){
dp[i][j][h]=dp[i-1][j][h];
if (j&&j<=i) dp[i][j][h]=min(dp[i-1][j-1][h]+(long double)(arr[i].x)/(use+1),dp[i][j][h]);
if (arr[i].y!=-1&&h&&h<=i&&j<=i&&j){
dp[i][j][h]=min(dp[i][j][h],dp[i-1][j-1][h-1]+(long double)(arr[i].y)/(h));
}
// cout<<dp[i][j][h]<<' ';
}
// cout<<'\n';
}
// cout<<'\n';
}
// cout<<'\n';
return dp[n][k][use];
}
bool cmp(pii a,pii b){
if (a.y!=b.y) return a.y<b.y;
return a.x<b.x;
}
signed main(){
fast
cout<<fixed<<setprecision(20);
cin>>n>>k;
for (int i=1;i<=n;i++) cin>>arr[i].x>>arr[i].y;
sort(arr+1,arr+1+n,cmp);
for (int i=0;i<=k;i++){
ans=min(ans,solve(i));
}
cout<<ans<<'\n';
}
